Integrated reinforced plastic unit and method and apparatus for making the same

ABSTRACT

An integrated plastic unit and molding or thermoforming process and apparatus for producing the plastic unit from heated thermoplastic sheet material, such as polyethylene. The heated thermoplastic sheet material is placed over reinforcing forming members disposed on spacers which space the reinforcing forming members from the face of a mold, and the reinforcing members extend over substantially the entire face of the mold. The heated sheet material is then forced over the reinforcing forming members and over the face of the mold, such as by vacuum forming, to provide a generally flat surface extending in one plane and a bridging or web surface encapsulating the reinforcing forming members to provide a fused ribbed substructure of the thermoplastic sheet material reinforced by the forming members extending in a plane generally perpendicular to the flat surface. The reinforcing forming members may be metal members such as bars, wire, strip or rods, arranged in a grid-like network. The mold may be flat or of bowed configuration. The product is particularly utilized as a pallet for transportation by forklift trucks in which event legs are provided for the unit.

United States Patent 1 Story [75] Inventor:

Fla.

[73] Assignee: Plasteel Industries Fort Lauderdale, Fla.

[22] Filed: March 2, 1971 [21] Appl. No.: 120,086

Incorporated,

Related U.S. Application Data [63] Continuation-in-part of Ser. No.66,748, Aug. 25, 1970, and a continuation-in-part of Ser. No. 66,749,

Aug. 25, 1970.

[52] U.S. Cl ..108/51, 264/92 [51] Int. Cl. ..B65d 19/00 [58] Field ofSearch ..108/51, 52, 53, 54, 55, 56,

William K. Story, Wilton Manors, A

Primary Examiner-Francis K. Zugel Assistant Examiner-Garry MooreAtt0rneyAndrus, Sceales, Starke & Sawall [57] ABSTRACT An integratedplastic unit and molding or thermoforming process and apparatus forproducing the plastic unit from heated thermoplastic sheet material,such as polyethylene. The heated thermoplastic sheet material is placedover reinforcing forming members disposed on spacers which space thereinforcing forming members from the face of a mold, and the reinforcingmembers extend over substantially the entire face of the mold. Theheated sheet material is then forced over the reinforcing formingmembers and over the face of the mold, such as by vacuum forming, toprovide a generally flat surface extending in one plane and a bridgingor web surface encapsulating the reinforcing forming members to providea fused ribbed substructure of the thermoplastic sheet materialreinforced by the forming members extending in a plane generallyperpendicular to the flat surface. The reinforcing forming members maybe metal members such as bars, wire, strip or rods, arranged in agrid-like network. The mold may be flat or of bowed configuration. Theproduct is particularly utilized as a pallet for transportation byforklift trucks in which event legs are provided for the unit.

8 Claims, 10 Drawing Figures Jan. 16, 1973 PATENTEDJ/m 16 1975 SHEET 1[IF 3 INVENTOR WILLIAM K STORY ATTORNEYS PATENTEDJAN 16 I975 SHEET 2 BF3 Z f Ml//////A f////1V //ll ////H /////H ////Jf///// lNVENT OR WILLIAMK. STORY ATTORNEYS PATENTEDJAH 16 I975 3.710.733 sum 3 or 3 L I. a! 2524 INVENTOR WILLIAM K STORY ATTORNEYS INTEGRATED REINFORCED PLASTIC UNITAND METHOD AND APPARATUS FOR MAKING THE SAME This application is acontinuation-in-part of application Ser. No. 66,748, entitled StructureMolding Process, filed Aug. 25, i970, by the present applicant; andapplication Ser. No. 66,749, entitled Plastic Pallet Encompassing MetalForm, filed Aug. 25, 1970, by the present applicant.

BACKGROUND OF THE INVENTION This invention relates to integratedreinforced plastic units which can be utilized for various structuraland load bearing purposes, and is particularly useful as the deck of apallet, for lifting and transportation by forklift trucks.

Many attempts have been made to produce a panel of synthetic materials,such as plastics, or the like, which might serve as a structural memberor work receiving member. In the case of the use of such panels forpallets, for example, to increase strength, such synthetic pallets havebeen molded into a ribbed-type shape with elaborated molds beingrequired to produce the rib-like structure which was necessary forincreasing the strength of the synthetic pallet. This created a palletin which the loading surface had rib-shaped indentations from themolding process, and yet the pallet was not rigid, and flexed underload.

The present invention overcomes these problems while increasing thestrength of a synthetic pallet, such as of plastic, in which elaboratemolds are not required for the construction, and in which the pallet hasa substantially rigid flat working and lifting surface. The product ofthe invention is lightweight while still retaining structural liftingstrength.

BRIEF DESCRIPTION OF THE INVENTION The invention is directed to anintegrated plastic unit and to the process and apparatus for producingsuch unit. The integrated ,unit essentially consists of two parts,namely, a generally flat panel section or deck,

and a ribbed substructurewhich extends from the flat section andprovides the rigidity for the unit. Under one method of producing theintegrated plastic unit, a vacuum mold is provided which has a pluralityof generally small holes therein through which a vacuum may be createdat the face of the mold. In addition, the mold has a plurality ofspacers on its face across which reinforcing forming members, such asmetal bars and rods, are placed in a crisscrossed fashion to locate themsubstantially over the entire face of the mold in a grid or lattice-likenetwork and spaced from the face of the mold. A thermoplastic sheet isthen clamped along its edges and is heated. After heating, the sheet isdrawn over the mold, either by pulling it over the mold and thereinforcing forming members or by raising the mold and the reinforcingforming members into the sheet. This results in sealing the edgeportions of the sheet to the sides of the mold to provide an air-sealedspace between the sheet and the mold. The air is then evacuated fromthis space by pumping the air therefrom out through the holes in themold. This creates a lower pressure in the described space with respecttothe atmospheric pressure on the outer side of the sheet and the vacuumaction so draws the heated material over the reinforcing forming membersthat, adjacent the vacuum side, the surface created on the face of themold will be flat, while above the flat surface, the plastic materialwill be contoured around the reinforcing forming members to encapsulatethe same and thereby providing a ribbed substructure with the plasticmaterial disposed as a bridge or rib between the reinforcing formingmembers and the flat surface of the unit. In use, the flat side will bethe load bearing and positioning side, in the event the deck of the unitis used as a pallet or the like, for the materials to be transportedwhile the ribbed side will be engaged by a forklift vehicle or the like.In the event the unit is used as the deck of a pallet, integral legs,forv example, may be molded from the heated material on the ribbed sideof the deck at a sufficient height above the ground or floor to receivethe lifting arms of a fork truck or the like. The rib-like substructureis preferably a combination of metal rods and rectangular bars asdescribed. However, even a mesh structure, such as a widely threadedwire or screen, could be used as the'reinforcing forming means, ornon-metallic materials may be employed, such as of plastic or fibrousmaterial. In any event, the material utilized, when in place over themold, should be rigid or taut, and spaced from the mold a sufficientdistance to provide a form around which the thermoplastic sheet can beforced or flowed, so as to encapsulate the form and provide a bridge orrib between the form and the generally flat surface of the integratedunit. The form remains within the plastic material to act as areinforcement for such material.

The spacers referred to above also act as fillets to prevent the plasticmaterial as it flowsfrom thinning out to such an extent as to tear holesin it. Additional fillets of lesser height may be provided beneath theintersection of the bars and rods of the reinforcing forming members todecrease the flow of the plastic material in these areas where theflowing material meets.

DESCRIPTION OF THE DRAWINGS The drawings illustrate the best modepresently contemplated of carrying out the invention.

In the drawings:

FIG. I is a perspective view illustrating a thermoplastic sheet whichhas been heated and clamped in position to receive a flat mold andreinforcing forming members;

FIG. 2 is a view similar to FIG. I in which the mold is bowed in onedirection and has pallet leg formers thereon;

FIG-3 is a perspective view of a mold spacer;

FIG. 4 is a perspective view of a button-like fillet;

FIG. 5 is a perspective view with parts in section illustrating thesheet sealed to the mold and extending over a leg former with a vacuumpartially applied;

FIG. 6 is a section taken on line 6-6 of FIG. 1;

FIG. 7 is a perspective view of a completed pallet;

FIG. 8 is a perspective view with parts in section of a part of a panelor deck as it appears when the forming operation is completed andwithout any legs molded thereto;

FIG. 9 is a perspective view of a welded'grid or reinforcing formingmembers supported only on the periphery of a mold; and a FIG. 10 is aview of a mold illustrating the use of a non-metallic cord-likematerial.

Referring to the drawings, there is illustrated in FIGS. 1 and 2, thevacuum molding or thermoforming apparatus of the invention and the sheet1 of the preheated plastic material or the like, which is to be formedinto the desired integrated plastic unit. In FIG. 1, the mold 2 consistsof a metal plate of aluminum or the like, of the size and shape of theintegral reinforced plastic unit, which is to be produced. The mold 2rests upon the vacuum box 3, which is connected to a pump or the like,not shown, and box 3 is provided with an opening, not shown, to theinner surface of mold 2, so that a pressure differential may beestablished on the face of the mold when the molding operation is beingeffected. Mold 2 is provided with a plurality of small holes 4, as seenin FIG. 6, so that the air may be evacuated from the face of the moldwhen sheet 1 is sealed to it for thermoforming.

FIG. 2 illustrates a bowed or curved mold 5 which has a box 3corresponding to that of mold 2 and likewise is connected to a powersource for evacuation of the surface of the mold 5 through the smallholes 7 therein and which are interspaced throughout mold 5.

The small holes in molds 2 and 5 have a diameter of the order of 0.012to 0.125 inches.

As described, FIG. 1 illustrates the generally flat mold 2, whereas FIG.2 illustrates the curved or bowed mold 5. However, the faces of themolds may take other contours than those shown, depending upon theintegrated plastic product which it is desired to mold. If the flat orstraight mold 2 is employed to form the heated sheet 1 into the productdesired, it has been found that it may be necessary to straighten thefinal product since the shrinkage of the material of sheet 1 uponcooling may cause the edge portions of the deck or panel to curveupwardly, which then requires flattening for proper utilization of theproduct. However, if a bowed or curved mold 5 is employed, when theformed material of heated sheet 1 cools, the final product will be in astraight condition so that a final flattening operation may beeliminated. The radius of the bow in mold 5 will depend on the size andshape of the mold, the composition of the material employed in sheet 1,and the size and shape of the reinforced forming members. When the bowedmold 5 is utilized, sheet 1, as shown in FIG. 2, is clamped in thegeneral bowed shape of mold 5. I

The faces of molds 2 and 5 are provided along spaced longitudinal andtransverse lines with spacer members 8, which project away from the faceof molds 2 and 5, a distance of approximately 1% inches and may be ofthe configuration shown in FIG. 3. The spacers 8 taper inwardly from thebase to the free ends thereof so that the plastic material to be formedcan readily However the spacers 8 in the forming operation, and also thetaper permits the product formed on the mold to be more readily removed.The spacers 8 are provided with a relatively deep notch 9 in onedirection to receive respectively, flat metal bars 10 which extend inone direction across the face of the molds, and a relatively shallownotch 11 located above notch 9, which extends in each spacer 8transverse to the notch 9. The shallow notches 11 receive the metal rods12, which lie above bars 10 and extend transversely of bars 10. Thenotches 9 and l 1 hold therespective bars and rods securely in place ina grid-type network and in spaced relation to the face of molds 2 and 5,so that the plastic material during forming can flow down the sides andunder the bars 10 and rods 12, and over i the face of the molds 2and 5.Satisfactory results have been obtained when the bottom of the deepnotch 9 is approximately one-half inch from the face of molds 2 and 5 tothereby provide a spacing of this dimension between the reinforcingforming members provided by bars 10 and rods 12 and the face of themolds. The distance of the reinforcing members from the face of themolds depends upon the surface thickness to be created. In order tostrengthen the integrated reinforced plastic unit, the edge portions areprovided with the bordering or perimeter bars 10 which are supported onspacer members 8 along the edge portions of molds 2 and 5.

In the bowed mold 5, illustrated in FIG. 2, the bars 10 are straight butthe rods 12 are curved to the general contour of mold 5 and in this moldthe bordering bars 10 are also curved to the general shape of the bow ofmold 5 whereas all the other bars 10, including the bordering bars 10 atthe edge portions of the mold 5 extending transversely of the bow orcurvature of the mold are straight. When the material of sheet 1 ismolded into place, the shrinkage of the material in sheet 1 straightensthe bowed bordering bars 10 and the bowed rods 12 so that the deck orpanel of the product will lie in a substantially flat plane.

In order to prevent excessive thinning out of the material of plasticsheet 1 beneath the-cross-over areas of the bars 10 and rods 12, conicalbutton-like fillets 13, as especially illustrated in FIGS. 4 and 6, maybe secured to the molds 2 and 5 to dam the flow of the plastic materialat these areas.

Sheet 1 is generally of a thermoplastic material such as polyethylene,polystyrene, acrylonitrile-butadiene styrene, polyvinyl chloride,cellulose-acetate-butyrate, polypropylene, acrylics and the like. Theheating of sheet 1 is not shown, since this is well known and may beaccomplished in numerous ways, either separately or on the mold. Duringheatingand assembly of sheet 1 with, for example, the mold 5, the edgesof sheet 1 are clamped and held by the clamps 14 which are shown in partin FIGS. 1, 2 and 5 of the drawings. In FIG. 1, since the sheet 1 isstraight, the clamps 14 would be straight whereas the clamps 14 would bebowed in one direction to shape sheet I to the bow of mold 5. The sheetI, after heating, is in a pliable condition so that it will readily flowwhen pressure is applied to it, 'but remains rigid enough so that it canbe held by the clamps 14. The temperature of the sheet 1 will varydepending on the composition of the material of sheet 1 and thethickness of the sheet. The thickness .of sheet I will be governed bythe integrated reinforced plastic unit which it is desired to produce,depending on such factors as the weight, thickness, and strength ofmaterial requirements in the final unit, and economic requirements. Apolyethylene sheet of one-fourth inch in thickness hasproducedsatisfactory pallets.

The preheated sheet 1 as illustrated, for example in FIG. 2, is slightlygreater in size than mold 5 so that clamps 14, as shown in FIG. 5-, candraw sheet 1 over the edges of the mold and seal the edge portions 15 ofthe sheet which lies inside clamps 14 against the sides of the mold 5.This provides the space 16 between sheet 1 and the face 17 of mold 5which is sealed against entry of air. When a vacuum is then drawnthrough holes 7 in the mold 5, a lower pressure is established in space16 by evacuation of the air from space 16 compared to the pressure onthe outside of sheet 1, and the plastic sheet 1 is thereby forced towardthe mold by the greater atmospheric pressure. The

material of sheet 1 then flows around and underneath the reinforcingforming members provided by bars 10 and rods 12 to completelyencapsulate them. After the material of sheet 1 has flowed around thereinforcing forming members, the material is drawn to the face 17 of themold in such a manner as to form a flat surface directly adjacent theface of the mold and underneath the reinforcing forming members.

The bars 10 and rods 12 thus provide a form around which the material ofsheet 1 flows. Any pressure differential technique in which a uniformhigher pressure is applied to the exposed side of the preheated plasticsheet 1 than exists between sheet 1 and mold 5 to effect uniform flow ofthe material toward the mold, could be employed or mechanical meansmight be used to force the plastic sheet 1 to take the form of the moldand encapsulate the reinforcing forming members.

The material of plastic sheet 1, upon encapsulation of the bars 10 androds 12 or other reinforcing members which may be employed, is fused ormelded into a single, continuous rib 18, as shown in FIG. 8, which liesbetween the flat portion 19 of the deck or panel, and is uninterruptedby any hairline crevice or the like. Consequently, the ribs 18 and thebars 10 and rods 12 encapsulated therein, provide a grid-likesubstructure for flat portion 19 which gives substantial rigidity to thestructure. Slight depressions 20 also may be formed in the face of theunit by the spacers 8 and button-like fillets 13. However, thesedepressions do not affect the strength or usability of the completedunit.

The button-like fillets 13, previously described, act as dams to providefilleted corners 21 at the cross-over areas of the bars 10 and rods 12to supply strength at those areas in the plastic material of sheet 1which,

. without the use of fillets 13, may thin out to a point where thematerial would tear.

Although the bars 10 and rods 12 are shown crisscrossed at right anglesto each other, any arrangement of the forming means could be used, solong as the substructure is of a construction to strengthen the finalproduct. FIG. 10 illustrates another embodiment of the invention whereina fibrous cord 22, such as of nylon, glass, hemp or the like, isstretched taut over the mold 23 in a'diagonal pattern and secured to thespacers 24 shown as secured to the face of mold 23 to space cord 22 fromthe mold. A preheated sheet material, such as the thermoplastic sheet 1,is then formed about the cord 23, as previously described with respectto bars 10 and rods 12, to encapsulate the same and provide a ribbedstructure and a generally flat body portion or panel corresponding tothat shown in FIG. 8.

In the event that it is desired to make the integral reinforced plasticunit usable as a pallet, legs 25 may be provided in various ways on theribbed side of the panel or deck of sufficient height so that fork armsmay be easily moved in and out from under the unit.

The legs 25 shown in FIG. 7 are shown as having been integrally moldedinto the unit when it was formed. This is accomplished by providing thefluted leg formers 26 on the face of the mold such as are shown on thebowed mold 5. FIG. 5 illustrates the heated sheet 1 clamped intoposition over one of the fluted leg formers 26 on mold 5, and when thevacuum is drawn, the legs 25 are molded by the leg formers 26, with afluted construction to give them strength. Because there are legs 25adjacent to the edge portions of the pallet, it is desirable to providethe spacers 27 as a part of leg formers 26 to receive the bordering bars10 the same as spacers 8 which reinforce the edge or border portions ofthe deck of the pallet.

It may be desirable to provide the reinforcing forming members as awelded grid. This construction is illustrated in FIG. 9. There thecrossed pieces are corresponding metal bars 28 which are notched as at29 to lie at the same level where they cross and are joined together atthe notched crossing area by welds 30. The bars 28 are supported onspacers illustrated by spacer 31 which extend along the entire peripheryof the mold 32, and the holes 33 are provided in the spacers for drawinga vacuum along the edge of the mold. The bars could take otherconfigurations or be rod'like members and could be supported byintermittent spacers along the periphery of the mold 32 corresponding tothe spacers 8, or which may be mounted on the face of the mold as inFIGS. 1 and 2.

ln carrying out the method of the invention, the sheet 1 is initiallyheated to temperatures of around 275 F.,

depending on the composition of sheet 1. During the heating of thesheet, the reinforcing forming members, consisting of bars 10 and rods12, or similar type rigid or tautly held forming members, are laid intothe spacers 8 in a crisscrossed configuration. The heated sheet is thendrawn over the reinforcing forming members and the mold, such as mold 5,and the edge portions of sheet 1, are sealed to mold 5. A vacuum is thendrawn in the air-sealed space 16 between face 17 of the mold and theinside of sheet 1. The heated material of sheet 1 thereby is causedunder atmospheric pressure to flow and fuse together around thereinforcing forming members, so as to encapsulate them and'form into anuninterrupted rib section, as well as providing a flat surface over theface of the mold under the rib section. After cooling and removal fromthe mold, the completed unit has a'flat panel or deck section and anintegral substructure of grid-like appearance which provides substantialrigidity and strength to the unit. In addition, if metal members areemployed in the grid substructure, these are protected by theencapsulating plastic from corrosion in service. In the event legs arerequired to use the unit as a pallet or the like, these may beintegrally molded into the unit during the forming operation.

Although the description has been directed to a flat panel or deck, itis also contemplated that the panel or deck of the unit may be curved orof other contour such as a tub or tote tray. I'Iowever, in' any event,the line of support of the substructure would extend in a planegenerally perpendicular to the plane of the area on the panel or deckfrom which the ribs extend.

Various modes of carrying out the inventionare contemplated as beingwithin the scope ofthe'following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim: I

1. An integrated reinforced plastic unit which comprises generally rigidreinforcing forming means, a onepiece preformed thermoplastic sheet ofmaterial assembled with said reinforcing forming means with the firstportion of said sheet material extending in opposite directions in aplane parallel to and spaced from the reinforcing forming means andoverlying said reinforcing forming means to provide the outer surface ofsaid first portion as an exposed working surface, and a second portionof the thermoplastic material encapsulating the reinforcing formingmeans and providing fused ribs of the material extending from thereinforcing forming means in a plane substantially perpendicular to thefirst named portion and to the reinforcing forming means, said fusedribs combining with the reinforcing forming means to supply rigidity tothe plastic unit.

2. The integrated plastic unit of claim 1 in which the reinforcingforming means are members assembled in a criss-crossed configuration,and fillets of the sheet material provided at the crisscrossed areas ofthe members between the first and second portions of the sheet ofmaterial.

3. The integrated plastic unit of claim 1, in which the reinforcedplastic unit is a pallet and the reinforcing forming means are membersassembled in a crisscrossed configuration.

4. The integrated plastic unit of claim 1, in which the reinforcedplastic unit is a pallet and the reinforcing forming means are metalmembers.

5. The integrated plastic unit of claim 3, in which the reinforcingforming means are metal members which are welded together at the areaswhere they cross each other.

6. The integrated plastic unit of claim 1; in which the reinforcedplastic unit is a pallet and the reinforcing forming means are ofnon-metallic material.

7. The integrated plastic unit of claim 1, in which the thermoplasticmaterial is polyethylene, and supporting legs integrally molded as apart of the first-named portion of the material and projectingsubstantially perpendicular thereto a relatively short distancetherefrom to provide the plastic unit for use as a pallet.

8. A loading pallet comprising metal reinforcing members assembled in acrisscross configuration, a one-piece thermoformed sheet ofthermoplastic material with one portion encapsulating the reinforcingmembers and extending therefrom to a second portion of the sheet havinga generally flat configuration with fused ribs of the sheet materialdisposed between the encapsulating portion of the sheet material and thegenerally flat portion, and fillets of the sheet material provided atthe crisscross areas of the reinforcing members between the first-namedportion of the material and the generally flat portions.

* t t l

1. An integrated reinforced plastic unit which comprises generally rigidreinforcing forming means, a one-piece preformed thermoplastic sheet ofmaterial assembled with said reinforcing forming means with the firstportion of said sheet material extending in opposite directions in aplane parallel to and spaced from the reinforcing forming means andoverlying said reinforcing forming means to provide the outer surface ofsaid first portion as an exposed working surface, and a second portionof the thermoplastic material encapsulating the reinforcing formingmeans and providing fused ribs of the material extending from thereinforcing forming means in a plane substantially perpendicular to thefirst named portion and to the reinforcing forming means, said fusedribs combining with the reinforcing forming means to supply rigidity tothe plastic unit.
 2. The integrated plastic unit of claim 1 in which thereinforcing forming means are members assembled in a criss-crossedconfiguration, and fillets of the sheet material provided at thecrisscrossed areas of the members between the first and second portionsof the sheet of material.
 3. The integrated plastic unit of claim 1, inwhich the reinforced plastic unit is a pallet and the reinforcingforming means are members assembled in a crisscrossed configuration. 4.The integrated plastic unit of claim 1, in which the reinforced plasticunit is a pallet and the reinforcing forming means are metal members. 5.The integrated plastic unit of claim 3, in which the reinforcing formingmeans are metal members which are welded together at the areas wherethey cross each other.
 6. The integrated plastic unit of claim 1, inwhich the reinforced plastic unit is a pallet and the reinforcingforming means are of non-metallic material.
 7. The integrated plasticunit of claim 1, in which the thermoplastic material is polyethylene,and supporting legs integrally molded as a part of the first-namedportion of the material and projecting substantially perpendicularthereto a relatively short distance therefrom to provide the plasticunit for use as a pallet.
 8. A loading pallet comprising metalreinforcing members assembled in a crisscross configuration, a one-piecethermoformed sheet of thermoplastic material with one portionencapsulating the reinforcing members and extending therefrom to asecond portion of the sheet having a generally flat configuration withfused ribs of the sheet material disposed between the encapsulatingportion of the sheet material and the generally flat portion, andfillets of the sheet material provided at the crisscross areas of thereinforcing members between the first-named portion of the material andthe generally flat portions.